There are many systems which contain pipes carrying fluids at high pressure. In known steam-electric power plants, for example, water is circulated through a heat exchanger, such as a nuclear reactor core, situated in a pressure vessel, the pressure vessel being surrounded by a primary safety containment. Steam thus produced is taken from the pressure vessel through steam pipes (or lines) and applied to a steam turbine-generator often located somewhat remote from the pressure vessel. There are, of course, numerous other pressure pipes connected to the pressure vessel and located within the primary containment, such as coolant circulation pipes, and in the case of a nuclear steam generator, pipes for applying emergency coolant to the nuclear reactor core. The primary containment also contains other vital equipment such as sensing and measuring devices and electrical circuits connected thereto.
In the unlikely event that one of the pressure pipes should rupture or break, the large jet (or blowdown thrust) forces of the escaping high-pressure fluid may cause the pipe to whip, that is, to move in a direction which is at an angle to the original longitudinal axis of the pipe. If unrestrained, such a whipping pipe may strike other components, such as the containment, other pipes, instrumentation, electrical cables and the like, thus compounding the damage to the system.
It is therefore desirable to provide pipe restraint means which will limit the movement of a severed pipe and prevent impact damage to adjacent components. Desirably, such pipe restraint means should include the following features:
1. It should absorb the energy of the moving pipe, have high energy absorption capacity and high material efficiency;
2. It should provide a relatively large normal clearance between the restraint member and the pipe to allow normal unrestricted thermal pipe movement, to facilitate in-service pipe inspection and to allow use of standard pipe insulation material;
3. It should be of compact size because space in the primary containment is severely limited;
4. It should prevent localized restraint forces on the pipe to prevent premature pipe crushing and possible break-off whereby a broken-off end of a pipe could become a missile;
5. It should be readily removable for replacement or for pipe repairs;
6. It should minimize loading on the structure to which the pipe restraint is attached;
7. It should minimize pipe rebound; and
8. It should provide predictable energy absorption and load deflection behavior.
Previously considered pipe restraint means do not provide these desirable features. For example, rigid or elastic restraints are of large size, they interfer with normal pipe movements; they can cause pipe rebound and impose high loads on the pipe and restraint attachment structure. Another previous design involved the use of a relatively large amount of crushable material around the pipe. In addition to its excessive space requirements, this design interfers with pipe inspection and repairs. The present invention is, of course, distinct from pipe hangers (saddles or cradles) such as shown, for example, in U.S. Pat. Nos. 2,291,148; 3,623,686; 3,539,136 and the like. Such hangers are in contact with the pipe since their purpose is to support the pipe in normal operation. They are not designed to be normally out of contact with the pipe nor to absorb the pipe whip energy of a ruptured or broken pipe.